1. Field of the Invention
The present invention relates to an image display device, and more particularly to an image display device for displaying an image by irradiating a projected plane with laser light.
2. Description of the Background Art
Image display devices displaying images by applying laser light onto projected planes such as screens or walls include so-called laser projectors. In a laser projector, laser lights of three primary colors of red, green and blue need to be prepared in order to reproduce images in full color. The configurations concerning image display using laser light in this manner are proposed in the followings.
Japanese Patent Laying-Open No. 2003-005110 discloses a configuration in which the timing of driving a light source and the modulation timing are synchronized with each other. For this purpose, a special pattern for detecting the quantity of light is prepared. A configuration to prevent this pattern from being projected is disclosed.
Japanese Patent Laying-Open No. 2007-114526 discloses a configuration to obtain information about positional displacement of scanning of a light spot.
Japanese Patent Laying-Open No. 2007-003687 discloses a configuration in which when an image is displayed by two-dimensional scanning, driving of a light source means is controlled by detecting failures of a scan means and the light source means based on an output signal from a light-receiving means.
Japanese Patent Laying-Open No. 2005-242036 discloses a configuration to correct the positions of light spots by multiple light sources.
Japanese Patent Laying-Open No. 2005-077431 discloses an apparatus capable of accurately detecting a synchronization signal to allow images of good image quality to be displayed and viewed.
The apparatus such as a laser projector which displays an image by applying laser light onto a projected plane includes, for example, a laser diode as a light source. It is known that when a laser diode is powered for a long time, the temperature of the laser diode itself changes and thus the response characteristic changes with the temperature change. In other words, the quantity of light output with respect to the level of current applied to the laser diode for driving decreases with increasing temperature. As a result, the quantity of light which should be achieved for a prescribed gradation at room temperature cannot be achieved at a temperature rise, so that the image quality of display images is reduced. Therefore, it has been desired that the image quality of display images is appropriately maintained with a simple configuration, irrespective of such a response characteristic change.
In this respect, Japanese Patent Laying-Open No. 2003-005110 proposes that special pattern information is prepared, the quantity of light output by driving a laser diode according to the pattern information is monitored, and the reference value of the driving current of the laser diode is updated based on the monitor result. However, special pattern information needs to be prepared. Moreover, special control is required so that an image according to the pattern information is not displayed, thereby complicating the configuration.
Furthermore, Japanese Patent Laying-Open Nos. 2007-114526, 2007-003687, 2005-242036, and 2005-077431 as described above do not disclose a specific technique for correcting output variations of the light source.